1. Field of the Invention
The invention relates to a control apparatus for an internal combustion engine and a control method for an internal combustion engine.
2. Description of the Related Art
A control apparatus for controlling operation of an electronic throttle valve for controlling an amount of air drawn into a combustion chamber of an internal combustion engine (intake air amount) is disclosed, for example, in Japanese Patent Application Laid-Open No. 10-89140. In this control apparatus, opening of the electronic throttle valve is controlled in accordance with depression stroke of an accelerator pedal (accelerator depression stroke). For instance, if a required torque increases as a result of an increase in accelerator depression stroke, an amount of intake air is increased by increasing an opening of the electronic throttle valve, while an amount of fuel injected from a fuel injection valve (fuel injection amount) is increased as well. Thus, the required torque is output from the internal combustion engine.
Fuel is injected from the fuel injection valve for a relatively short period after closure of an intake valve. An intake air amount must be estimated from an opening of the electronic throttle valve long before the intake valve is closed, for example, before the intake valve starts opening, and a fuel injection amount must be determined, on the basis of the intake air amount thus estimated, such that a desired air-fuel ratio is obtained. In this case, therefore, a fuel injection amount is determined before an intake air amount is confirmed.
For example, however, if a fuel injection amount is determined according to the procedure mentioned above when an opening of the electronic throttle continues to be increased as a result of a continuous increase in required torque, an actual intake air amount deviates from an intake air amount estimated at the time of determination of the fuel injection amount. Therefore, a desired air-fuel ratio cannot be obtained.
In Japanese Patent Application Laid-Open No. 10-89140, therefore, an opening of an electronic throttle valve is not immediately increased even after an increase in accelerator depression stroke. Instead, the opening of the electronic throttle valve is increased after the lapse of a certain delay period. The delay period is set such that the electronic throttle valve assumes an opening corresponding to an accelerator depression stroke at the time of determination of a fuel injection amount when an intake valve is closed. A fuel injection amount is determined on the basis of an opening of the electronic throttle valve corresponding to an accelerator depression stroke. This means that a fuel injection amount is determined on the basis of an opening of the electronic throttle valve at the time of closure of the intake valve. Thus, a desired air-fuel ratio is obtained.
Thus, in order to obtain a desired air-fuel ratio during a continuous change in intake air amount, it is necessary to precisely estimate an intake air amount and to determine a fuel injection amount.